The present invention pertains to ambient and low temperature curable polymer mixtures consisting of a first polymer containing reactive or catalytic amino groups and a second polymer containing oxirane functionality which are one package stable and are useful as coatings and adhesives. Although amino functional polymers are known to react with oxirane containing polymers, in the past, there has been great difficulty in keeping such system fluid and without appreciable coreaction in a single package.
In the past, separate solvent solutions of epoxy and amino polymers and oligomers have been blended and applied as surface coatings and adhesives. These are two package systems generally having limited pot lives measured in hours. Once the solutions are mixed, individual polymer molecules diffuse and more or less randomly mix allowing the coreactants to come into contact. The cure reactions start independently of whether the mixture is applied to form the surface coating or cover the adherant surface. Within a relatively short period of time, the viscosity of the mixture in the pot increases to the point that film application is no longer possible. A solution to this problem in the case of room temperature curable coatings has been to prereact a secondary amino group with a ketone to form a ketimine prior to mixing in the oxirane containing polymer. After the film is applied, atmospheric moisture causes the ketimine to decompose yielding the reactive amino group and the ketone, allowing the normal cure reaction to occur. There are two main drawbacks to this type of system. First, it is limited to nonaqueous systems and, second, ketone solvent is released upon cure. More recently to reduce solvent pollution, two other approaches have been used. These are to use lower viscosity amino and oxirane containing mixtures that require little or no solvent or to use water as the solvent. Neither approach has yielded stable one package systems that cure at room temperature. In the former case it is obvious that molecular mixing brings the reactants into immediate contact. In the latter case, amino and oxirane functional oligomers and polymers are emulsified separately and blended just before application. Generally, the individual emulsified particles consisting of many individual molecules are not stabilized well enough to prevent co-coagulation with each other. While attempts have been made to reduce the rate of coagulation, there is a second problem which has generally not been appreciated. The emulsified particles may be made relatively stable but individual molecules from them diffuse through the aqueous medium to particles containing the coreactant. This causes the particles to become cross-linked. The result is stabilized rubber particles which will not coalesce or further cross-link to form a servicable coating or adhesive.
We have discovered that if the amino and oxirane functionality is attached to nearly completely water insoluble polymers and the particles are mutually stabilized to prevent coagulation, then the molecular diffusion process can be stopped and a one package system is produced. Upon film application, the water medium evaporates and the particles with coreactive functionality come into intimate contact and cross-link to form a tough, solvent and water resistant coating or adhesive. The preferred method of dispersing the water insoluble polymer into water is to use latex polymerization methods. This provides very small, relatively uniform, stabilized water insoluble polymer particles. Such latex mixture can be compounded in the usual ways to give surface coatings. These and other advantages will become more apparent from the detailed description and the illustrative examples.